Unit for reproducing transparent originals, or the like

ABSTRACT

A compact optical bench type unit for making selected color-component records of color transparencies for use in color printing comprises a light source with a rotary filter disc for directing a beam of selectively colored light through a light condenser which converges the beam through a color diapositive to be reproduced and into the objective of a camera. The condenser, possibly formed of Fresnel lenses, is of large dimensions to accomodate large diapositives, and the camera objective has a relatively short focal length. Chromatic aberration of the condenser is corrected by moving the light source in correspondence with rotation of the filter disc, or by selectively inserting correcting lenses in the beam.

This is a division of application Ser. No. 746,301, filed Dec. 1, 1976,now U.S. Pat. No. 4,110,036, issued Aug. 29, 1978.

This invention concerns a unit for reproducing transparent originals,notably for making colour selections, comprising a light generatorproducing a beam of light directed via a light condenser to a camera,and a carrier for supporting an original in said beam of light.

There are many units for reproducing transparent photographic originalson the market. The invention particularly concerns such units in theform of optical benches used to make colour selections which are thenhalf-toned for reproduction of colour diapositives by printing presses,the reproduction being either quadrichrome (red, green, white and bluecomponents) or trichrome (red, green and blue components). Opticalbenches used for making colour selections enabling high qualityreproduction are large apparatus (on average, 3 meters long) and mustgenerally be located in a dark room. Such optical benches have anoptical condenser with a focal length of at least 400 mm and a camerawhose objective also has a focal length of 400 mm. These dimensions arenecessarily dictated by the dimensions of the originals to bereproduced, namely transparent films of up to 40 cm diagonal.

An aim of the invention is to provide a unit or optical bench for thereproduction of transparent originals which is of substantially smallerdimensions than the comparable known units and which does not have to beplaced in a dark room, while having the same refinements and quality ofreproduction as the known units or optical benches of greaterdimensions.

To offer the same possibilities of use, the unit according to theinvention will have an optical condenser with a focal length of about400 mm, which permits the reproduction of large originals. However, itwill be relatively small, i.e. its length need be no greater than 1.20meter. To enable this, the camera objective will have a focal length of80 to 100 mm at the most, instead of 400 mm.

To achieve this aim, the unit according to the invention ischaracterized in that it comprises means for correcting chromaticaberration controlled in relation to changes of colour of the beamemitted by the generator.

In a preferred embodiment of the invention, the means for correctingchromatic aberration comprise a motor arranged to provide a relativemovement between the camera and the light generator to make the point ofconvergence of the beam into the camera coincide with the optical centreof the camera objective. The motor controls movement of the lightgenerator at the same time as a member for positioning filters ofdifferent colour in the beam.

The light generator is moved by means of a disc driven by the motor,this disc being connected to the light generator by a crank whose freeend is pivotally mounted on a support fixed on at least one horizontalrail on which the light generator can slide, the motor also beingconnected to the filter-positioning means which is in the form of afilter disc.

Driving of the motor can be controlled by an electric circuit comprisinga printed circuit plate having conductive "positioning" area, this platebeing placed adjacent the disc which moves the light generator by thecrank, a sliding contact turning with this disc coming to contact theconductive areas of the plate to deliver an electric signal to thecircuit controlling the motor.

The accompanying drawings show, by way of example, an embodiment of aunit for reproducing transparent originals according to the invention,as well as two variations. In the drawings:

FIG. 1 is a schematic side elevational view of the reproduction unitwhich is adapted for the taking of colour selections from a colourtransparency;

FIG. 2 is a schematic diagram showing the chromatic aberration producedin the diametral plane of the objective in the reproduction unit whenblue, green and red filters are placed in the beam of light;

FIG. 3 is an underneath plan view of a sliding chassis carrying thelight generator and filters of the unit of FIG. 1;

FIG. 4 is a cross-section along line IV--IV of FIG. 3;

FIG. 5 is a diagram of an electric circuit for controlling movement ofthe chassis of FIGS. 3 and 4;

FIG. 6 is an enlarged-scale view of a printed circuit located under thesliding chassis of FIG. 3;

FIG. 7 is a view of a first variation of a part of the unit of FIG. 1;and

FIG. 8 is a view of a second variation of a part of the unit of FIG. 1.

The reproduction unit shown in FIGS. 1 to 6 comprises (FIG. 1) alight-generator chassis 1 arranged to slide on two parallel horizontalguide rails 2, 3 forming an optical bench and united by a chassis 4 ofan optical condenser and by an end cross-piece 5. The optical bench ofFIG. 1 rests on a working table, not shown, by rubber feet 6, 7 underthe chassis 4, and 8, 9 under the crosspiece 5. The upper part ofchassis 4 carries an optical condenser 10 having a lens system and arear light shield 11 in the form of a box which is connected to thelight-generator chassis 1 by a bellows 12. The chassis 1, which will bedescribed in detail with reference to FIGS. 3 to 6, carries a dischargetube 13, a setting lamp 14, a diaphragm 15, and a filter disc 16 havinga sighting aperture and at least one red, green and blue filter, as wellas a motor unit 16' connected to control the filter disc 16 and to movethe chassis 1 on the rails 2, 3. Following the optical condenser 10 isplaced an original-support 17 mounted on a chassis 18 having a controlhandle 19 enabling the support 17 to be moved along a rack, not shown,fixed on one of the guide rails 2, 3. The support 17 is connected to oneside to the optical condenser 10 by means of a bellows 20 and on itsother side to an objective 21 of a still camera 22 by a bellows 23. Theobjective 21 is fixed on the two rails 2, 3 by a support 24 and isconnected to the camera 22 by a bellows 25. Camera 22 is fixed on asupport 26 comprising a control handle 27 enabling the camera to bemoved along a rack, not shown, fixed on one of the rails 2, 3. Thecamera 23 is of the type described in Swiss Pat. No. 595,610 andcorresponding U.S. Pat. No. 3,984,849, and its objective 21 is aconventional one with an incorporated diaphragm 106 and having a focallength of about 80 mm. The camera 22 is fitted with a photo-electric 100arranged to be movable to any point of the plane 101 in which the imageof the original is formed ("film plane") so that the cell 100 canmeasure the intensity of the light from the discharge tube 13 at anypoint of the plane 101 of the image. This briefly-described cell isimportant, as it enables a light setting as will be explained withreference to FIGS. 3 and 4. The camera described in the stated patentsis a 6/6 camera adapted to take colour selections and is able to receivecorrecting masks. However, it is clear that it may be replaced by otherknown cameras with an appropriate objective.

The optical condenser 10 comprises a lens system with a focal distanceof 350 to 400 mm.

The originality of the optical bench of FIG. 1 resides in the fact thatan optical condenser 10 having a focal length of 350 to 400 mm iscombined with a camera with an objective of 80 mm focal length. Thiscombination is contrary to the practices heretofore followed by personsskilled in the art, but it enables the optical bench to have a length ofonly 1.25 meters whereas all of the comparable prior-art optical bencheshave lengths of two meters or more. Although it has a length of only1.25 meters, the optical bench of FIG. 1 nevertheless enables thereproduction of originals with a diagonal of up to 40 cm with a greatersharpness than that obtained with the conventional optical benches. Thisperformance is enabled thanks to a correction device explained in detailwith reference to FIGS. 2 to 4.

Operation of the optical bench of FIG. 1 will be described later.

FIG. 2 schematically shows the chassis 1 carrying the discharge tube 13,diaphragm 15 and filter disc 16. A beam of light 30 emitted by tube 13passes through the diaphragm 15 and a blue filter 31 of filter disc 16to condenser 10 which focuses it at P_(B), the converging beam alsopassing through an original carried by support 17. When the blue filter31 is replaced respectively by a green filter and a red filter, whilemaintaining the setting of the optical bench, the beam 30 is focused atpoints P_(V) and P_(R) respectively. In the instance of the 1.25 meteroptical bench of FIG. 1, the distances between the points P_(B), P_(V)and P_(R) is of the order of a centimeter. Thus, it is clear that if theoptical bench of FIG. 1 is set for white light (which settingcorresponds approximately to the setting for green light), the pointP_(V) of FIG. 2 wil be at the focal point of the objective 21 of camera22 and the image of the green selection in the plane of film in thecamera will be sharp. To the contrary, when the blue filter or redfilter is used, the point P_(B) or P_(R) will not be at the centre ofthe objective 21 but respectively in front of and behind it.Consequently, the image of the blue or red component will be blurred andwill have a lighting fault between the centre and the edges of the imagein the film plane of the camera.

The chromatic aberration effect which has just been explained is all themore critical as the focal length of the camera objective decreases. Inlarge installations several meters long, whose camera objective has afocal length of about 400 mm, chromatic aberration is not critical anddoes not require correction, apart from the usual masking correctionscarried out by the operator. To the contrary, in the installation ofFIG. 1 with a camera objective of relatively short focal length, acorrection is necessary. Persons skilled in the art will realize thatthe chromatic aberration cannot be corrected by changing the distancesbetween the camera and its objective or between the camera and theoptical condenser, since this would alter the dimensions of the colourselections. The applicant thus sought, against the advice of all theexperts consulted, to carry out a correction applied to the lightsource. Tests carried out with a light generator having a control deviceas shown in FIGS. 3 to 6 have given good results.

FIGS. 3 and 4 show the right-hand part of the optical bench of FIG. 1.The optical condenser 10, mounted on the guide rails 2, 3, has its rearlight shield 11 connected by bellows 12 to a front wall 35 (FIG. 4) ofthe light-generator chassis 1. The light-generator chassis 1 is in theform of a box with upper and lower walls 36, 37 and an intermediatefront wall 38. The lower wall 37 is supported by four ball bearings 39,40, 41 and 42 sliding on the guide rails 2, 3, whereby thelight-generator chassis 1 can move along the guide rails 2, 3.

The filter disc 16 comprises a sighting aperture and blue, green and redfilters (not shown) equally spaced apart from one another, and issupported on a rotary axle 43 passing through wall 38. At the end ofaxle 43 is a bevel pinion 44 meshing with a similar pinion 45 fixed atthe upper end of a vertical rotary shaft 46. In its middle part, shaft46 has a toothed wheel 47 meshing with a toothed wheel 48 driven by amotor 49. The lower end of shaft 46 carries a driving disc 50 connectedby a pivoted crank 51 to a cross-bar 52 fixed on rails 2, 3 by means ofscrews 53, 54. The crank 51 is pivotally connected to the disc 50 andcross-bar 52 by respective pins 55, 56. Thus, when the motor 49 isstarted, the toothed wheel 48 drives shaft 46 via the toothed wheel 47.The shaft 46 rotatably drives, on the one hand, the disc 50 whichreciprocates the chassis 1 between two extreme positions and, on theother hand, the filter disc 16 via the bevel gear 44, 45. Starting andstopping of the motor 49 is controlled by a stationary printed circuit57 and a sliding contact 58 fixed on the disc 50 and arranged to set upselective electric contacts with the printed circuit 57. It can also beseen in FIGS. 3 and 4 that an opening 59 is provided in the lower wall37 of chassis 1 to permit passage of the periphery of the filter disc16, so that rotation of this disc can be controlled.

On the lower wall 37 of chassis 1 is mounted a tube-support in the formof an L-shaped bracket 60 having a setting screw 61 enabling thisbracket to be moved forwards or backwards on the chassis 1. On bracket60 is mounted the discharge tube 13 which in the illustrated embodimentsis an annular Xenon tube. At the centre of tube 13, the bracket 60 alsocarries a setting lamp 14. At the centre of the intermediate wall 38,between the filter disc 16 and the tube 13 and lamp 14, is the diaphragm15 having an actuating rod 62. As shown in FIG. 4, a beam of light 63emitted by the lamp 14 passes through the diaphragm 15 (regulation ofthe opening of which will be explained later), through one of thefilters of disc 16 and an opening 64 in the front wall 35 of chassis 1,to the optical condenser 10. On its upper wall 36, chassis 1 also has anopening 65 disposed above the tube 13 for the outlet of air heated bythe tube 13.

Persons skilled in the art will easily understand that the possibilityof moving the tubes 13 away from or towards the diaphragm 15 by means ofthe setting screw 61 of bracket 60 enables a constant luminous intensityto be obtained at any point of the plane of the film in the camera. Thisregulation of the luminous intensity to be constant at all points of thefilm will be explained in detail later. Also, it can be seen from FIG. 4that the arrangement of the motor 49, the filter disc 16 and its drivingmembers, and the driving disc 50 and its driving members can be adjustedso that when each of the filters and the sighting aperture of disc 16 isfacing the diaphragm 15, the position of the light-generator chassis 1on the guide rails is such that the chromatic aberration represented inFIG. 2 is compensated, i.e. the points P_(R), P_(V) and P_(B) arebrought to the same point corresponding approximately to the position ofpoint P_(V). Hence, the chassis 1 (FIGS. 1, 2 and 4) will be in anintermediate position when the green filter or the sighting aperture isfacing the diaphragm 15, in a forward position (relative to thedirection of the light beam) when the red filter is facing the diaphragm15 and in a rear position when the blue filter is facing the diaphragm15.

Control of displacement of the chassis 1 will now be explained in detailwith reference to FIGS. 5 and 6. These figures show the disc 50 and thesliding contact 58 which makes a selective electric contact between acentral circular electrically conductive area 65 and outer electricallyconductive contact area 66, 67, 68 and 69 of the printed circuit 57. Theareas 66, 67, 68 and 69 are connected (FIG. 5) to correspondingterminals 66a, 67a, 68a and 69a of a control switch 70. The area 66 andits terminal 66a correspond to an intermediate position of chassis 1,i.e. to setting for white light through the sighting aperture of thefilter disc 16. The area 67 and its terminal 67a correspond to anextreme rear position of chassis 1, namely a setting for blue light whenthe disc 16 places the blue filter in the light beam. Area 68 and itsterminal 68a correspond to another intermediate position of chassis 1,namely a setting for green light when the disc 16 places the greenfilter in the light beam. Area 69 and its terminal 69a correspond to theextreme forward position of chassis 1, namely a setting for red light,when the disc 16 is positioned to place the red filter in the lightbeam. The supply circuit of motor 49 shown by terminals 71 and 72 (FIG.5) is connected to positive and negative supply terminals 73, 74 via arelay 75 having a winding 76 which is energized when the sliding contact58 contacts one of the areas 66 to 69. The switch 70 is connected to thepositive terminal 73.

The control circuit of FIGS. 5 and 6 operates as follows:

Suppose that the switch 70 is on terminal 66a, as indicated by theunbroken arrow, i.e. corresponding to the sighting position (whitelight), in which the beam of light passes through the sighting apertureof the filter disc 16. The chassis 1 is in one of its intermediatepositions corresponding to the setting for white light (sighting). Allof the settings of the optical bench of FIG. 1 (placing of an originalin support 17; setting the position of support 17 on rails 2, 3, settingof the camera, etc.) are carried out by the operator. These settings arethe same as for known installations, and will consequently not bedescribed in detail.

Once the settings have been made, it is possible to proceed with takingof the colour selections. For this, the switch 70 is firstly placed ontothe terminal 67a, as indicated by the dashed arrow in FIG. 5, whichcorresponding to taking of the blue selection. When the switch 70 leavesterminal 66a, to go towards terminal 67a, the energization circuit ofwinding 76 is cut off and the blade 75a of the relay moves up. Motor 49starts up and drives the disc 50 clockwise (looking at FIG. 5). Thisturning of disc 50 drives the chassis 1 towards its rear limitingposition corresponding to the predetermined setting for blue light. Atthe moment when the sliding contact 58 turning with disc 50 arrives onthe area 67, as indicated by the broken arrow in FIG. 5, the winding 76is re-energized and pulls the blade 75a down, thus switching off themotor 49. The disc 50 thus stops with the chassis 1 in its rear limitingposition in which the blue selection is taken according to a well-knownprocedure. To pass to the following selection, the green selection, theswitch 70 is placed onto terminal 68a. The motor 49 starts and thechassis 1 is brought to its second intermediate position correspondingto the setting for a green selection, for which the point of convergenceof the beam of green light into the camera is exactly at the centre ofthe objective 21 (FIG. 1). Then, for the red selection, the chassis 1 isbrought to its extreme forward position, by placing the switch 70 onterminal 69a. FIG. 6 shows that the conductive areas 66, 67, 68 and 69are disposed at 90° to one another about the disc 50, the areas 67 and69 corresponding to the two extreme positions of chassis 1 for blue andred selections, while the areas 66 and 68 provide approximately the sameposition of chassis 1 for sighting (no filter) and for green selection.The positions of chassis 1 thus depend on the angular positions of theconductive areas 66 to 69 on the disc 50. The positions of chassis 1also depend on the position occupied by the camera 22 (FIG. 1). Personsskilled in the art will understand that if the elements of the bench ofFIG. 1, i.e. condenser 10, the support 17, and the objective 21 ofcamera 22 were moved towards the right to occupy only the right handhalf of the guide rails 2, 3, the corrections of chromatic aberrationprovided with the printed circuit of FIG. 6 would not be satisfactory.Thus, the printed circuit of FIG. 6 gives good results for anarrangement of the elements of the bench substantially as shown in FIG.1, i.e. as long as the camera 22 is positioned only between the endcross-piece 5 and the objective-support 24 (FIG. 1) and the positions ofthe objective 21, the original-support 17 and condenser 10 do not varygreatly from the positions shown. If other positions are previewed,different printed circuits will be provided, the conductive areas ofthese circuits having different angular positions to those of thecircuit of FIG. 6 as a function of the use of the bench.

Of course, the system for controlling the movement of the chassis 1,i.e. the motor and associated driving members as well as the circuit ofFIG. 5, may be replaced by a more elaborate system. One may for exampleprovide a stepping motor controlled by a memory storing correction datacorresponding to predetermined positions of the elements 1, 10, 17, 21and 22 on the bench of FIG. 1.

As mentioned above, the procedure for taking colour selections using thedescribed bench is the same as for conventional benches including, whenthe originals are of poor quality, masking operations. However, thequality of selections obtained with corrrection of chromatic aberrationsby displacement of the light-generator chassis 1 is such that masking isnot usually necessary. All of the setting operations are in generalcarried out using the lamp 14 (FIGS. 1 and 4) and the taking ofselections is carried out using the Xenon tube 13. As mentioned above, asetting can be carried out to make the light intensity equal for eachpoint of the film. This setting is carried out in the following manner:

A light beam emitted by an annular tube such as tube 13 gives, inprojection in a plane perpendicular to the axis of the beam, adistribution of light in the form of a circle in which the luminousintensity is greater at the edges of the circle than at its centre. Bymoving the tube 13 in the chassis 1 by means of the bracket 60 andsetting screw 61 (FIG. 4), it is possible to obtain, for a given openingof the diaphragm 15, an equal distribution of the light in the plane ofthe film of camera 22, i.e. with the luminous intensity equal for eachpoint of the film surface. If the camera 22 is of the type described inthe aforesaid Swiss Pat. No. 575 610 and U.S. Pat. No. 3,984,849, thisregulation of the intensity is easy to make. Once the opening of thediaphragm 15 is chosen, it suffices to make several light-intensitymeasurements by means of the aforementioned photo-electric cell 100 inseveral different positions of the image surface at the image 101, andto find the position of bracket 60 for which these measurements areapproximately the same as the centre and at the edges of the image.

The optical bench of FIG. 1 can be used to obtain perfectly sharpselctions, or selections with a desired blurring effect. For thispurpose, in front of the outlet of the diaphragm 15 of chassis 1, isplaced an unpolished glass 104, acting as a light diffuser. The cameraobjective 21 also has a diaphragm 106. If the diaphragm 15 of chassis 1is closed and the diaphragm 106 of the objective 21 opened while takingcare to carry out the setting of the light intensity by moving thesupport 60 (FIG. 4) and making measurements of the intensity at severalpoints of the image surface by means of the camera cell 100, selectionsof exceptional sharpness and hardness (contrast) will be obtained. Tothe contrary, to obtain blurred effects, it suffices to open thediaphragm 15 and close the diaphragm 106 of the objective 21. Of course,the operator can select any intermediate settings between the completeclosure and opening of the two diaphragms.

FIG. 7 shows a variation of part of the optical bench of FIG. 1 in whichthe correction of chromatic aberration is no longer achieved bydisplacing the light-generator chassis, but by adding correcting lensesbetween the objective 21 of camera 22 and the original-support 17. Inthis variation, the chassis 1 is fixed on the guide rails 2, 3. Themotor 16' is used only to turn the filter disc 16. The motor 16' iscoupled by means not shown to a motor 80 carrying on its shaft a disc 81placed between the objective 21 and the original-support 17. Thus, thebeam of light 82 from the light-generator passes through the condenser10 and an original carried by support 17 into the objective 21 whosecentre is represented by line 83. The disc 81 has two openings as wellas a converging lens 84 and a diverging lens 85. These are disposed onthe disc 81 so that the beam 82 passes through (a) an opening of disc 81when the sighting aperture or the green filter of disc 16 is placed inthe beam, (b) the converging lens 84 when the red filter of disc 16 isin the beam, and (c) the diverging lens 85 when the blue filter of disc16 is in the beam.

As already explained, regulation for the green beam correspondsapproximately to regulation for the beam of white light. Thus, it is notnecessary to make a correction for the green selection when the settingis carried out with white light. Hence, when the green filter of disc 16is in place, the filter 81, whose angular position is coupled with thatof the filter disc 16, will allow the beam to pass through an openingand converge to line 83 (centre of the objective 21). When the redfilter of disc 16 is in the beam, the disc 81 places its converging lens84 in the beam to bring the line 86 (whose point of convergence issituated on a line 87 beyond the centre of the objective) onto thecentre of the objective. When the blue filter of disc 16 is in the beam,the diverging lens 85 of disc 81 brings the line 88 (whose point ofconvergence is on a line 89 in front of the centre of the objective 21)onto the centre of the objective 21.

Of course, in the just-described variation, the converging and diverginglenses must be very precisely made and must be precisely placed in thelight beam, in order not to distort or displace the image projected ontothe film in the camera.

In order to considerably reduce the very high precision requirements forthe positioning of the lenses 84, 85 of the variation of FIG. 7, it ispossible, as shown in FIG. 8 for the second variation, to place thecorrection lenses in the light beam not between the camera and theoriginal-support, but between the light source and the condenser 10.FIG. 8 shows the light-generator chassis 1 with its light source 13,diaphragm 15 and filter disc 16 enabling filters of different colours tobe brought into the light beam 90 produced by source 13. As in the unitof FIG. 1, the light beam 90 passes through the optical condenser 10,then an original carried by the support 17 and enters the objective 21of the still camera. A second disc 91 is placed adjacent the filter disc16, between the latter and the condenser 10.

The disc 91 has two openings as well as a converging lens 92 and adiverging lens 93. As in the first variation of FIG. 7, the two openingsand the two lenses 92, 93 are disposed on the disc 91 so that the beam90 passes through (a) an opening when the sighting aperture or the greenfilter of disc 16 is in place, (b) the converging lens 92 when the redfilter of disc 16 is in the beam and (c) the diverging lens 93 when theblue filter of disc 16 is in place. Thus, with the disc 91 it ispossible to correct the point of convergence of the blue and red beams,so that this point of convergence coincides with the centre of objective21 for the three selections, red, green and blue. Also, as the disc 91is placed before the condenser 10 and the original-support 17, theprecision with which the lenses 92 and 93 must be placed in the lightbeam is less critical than for the variation of FIG. 7.

Instead of mounting the lenses 92, 93 on a separate disc 91 turning withthe disc 16, they can alternatively be carried by the disc 16 with thered and blue filters.

In the embodiment of FIGS. 1 to 6 and the variations of FIGS. 7 and 8,the light-generator chassis has a filter disc with three filters: red,green and blue. Of course, the disc may comprise supplementary filters,for example an orange filter, an olive filter or grey filters. Whensupplementary filters are provided, additional positions will beprovided on the control switch 70 of FIG. 5 and on the printed circuitof FIG. 6. As a variation, a supplementary disc carrying for example anorange filter or grey filters could be placed parallel to and adjacentdisc 16.

As previously mentioned, to permit the reproduction of large originals,the optical condenser must have a focal length of about 400 mm. Thecondenser 10 is thus formed of two large lenses. However, such acondenser weighs several tens of kilograms and is consequentlyexpensive, and also has the disadvantage of producing a sphericalaberration. Against the established usages, the applicant has carriedout tests with a condenser formed of two Fresnel lenses. Such acondenser has the advantage of low weight, relatively low cost and theproduction of relatively little spherical aberration. Its principaldisadvantage is the formation of dark concentric rings. However, theapplicant has remarked that excellent results can be obtained with acondenser formed of Fresnel lenses provided the original-support isspaced from the camera objective by a distance greater than the focallength of the objective. If this condition is satisfied, no Fresnel ringis visible on the colour selections. Thus, means may be provided forpreventing movement of the original-support closer to the cameraobjective than the focal point of the objective. As the focal length ofthe objective is short (about 80 to 100 mm) compared to that of thecondenser (about 400 mm), the mentioned condition for avoiding theformation of rings does not place any limitation to the use of the unitof FIG. 1.

What is claimed is:
 1. A unit for reproducing transparent originals, orthe like, comprising:a light generator for producing a beam of light;said light generator comprising a light source; a camera having a filmplane; a condenser for directing light to the film plane of said camera;a carrier for supporting an original in the beam of light from saidlight source; said light source being shaped in the annular form, withsaid annular source having an axis directed toward said camera objectiveand said light source directing light from said light generator towardthe film plane in said camera; said light source being movably mountedin said unit for enabling shifting of said light source toward and awayfrom said objective, for permitting compensating of the loss ofluminosity at the edges of the image due to vignetting of the cameraobjective and for obtaining also uniform light intensity on the filmplane in the camera.
 2. The unit according to claim 1, wherein saidannular source is a tubular lamp.
 3. The unit according to claim 2,wherein said tubular lamp is a discharge tube.
 4. The unit according toclaim 1, wherein said light generator further comprises a second lightsource located at the center of said annular light source and directinglight toward said camera objective.
 5. The unit according to claim 1,wherein said light generator includes an outlet for light; an adjustablelight generator diaphragm placed so that the light from said lightsource to said object passes through said light generator diaphragm. 6.The unit according to claim 5, further comprising filter means placednear to said light generator diaphragm.
 7. The unit according to claim6, wherein said filter means is placed in front of said light generatordiaphragm and between said light generator diaphragm and said objective.8. The unit according to claim 5, further comprising an adjustableobjective diaphragm near said camera objective; said light generatordiaphragm and said objective diaphragm being independently adjustable.9. The unit according to either of claims 5, 6, 7, or 8, furthercomprising a diffusing element placed in front of said light generatordiaphragm and between said light generator diaphragm and said objective.10. The unit according to claim 1, further comprising light intensitymeasuring means in said camera for measuring light intensity at variouslocations at the film plane.